Interleukin 4 (IL-40 plays several critical roles in the regulation of immune responses. This immunomodulatory cytokine is required for the production of antibodies of the immunoglobulin E (IgE) class, which are involved in allergic diseases and asthma. In addition, IL-4 regulates the development of subclasses of helper T lymphocytes, selectively promoting those which produce the TH2 spectrum of cytokines. However, the precise intracellular signal transduction pathways that link the IL-4 receptor with transcriptional regulation have not been characterized. In this regard, we have identified a nuclear protein termed NF-BRE (Nuclear Factor binding to a B lineage Regulatory Element), whose DNA binding activity is regulated by IL-4 treatment of normal lymphocytes. To study how IL-4 causes changes in lymphocyte function, we also identified a promoter which is involved in the control of immunoglobulin heavy chain class switching to IgE. This promoter, called the germline epsilon RNA promoter, is bound at regulatory sequences by NF-BRE. In studies on the structure of this protein, we find that NF-BFRE is a multi-subunit complex that contains a constitutive non- histone chromosomal protein, HMG-1 (Y). Our studies on the control of the germline epsilon RNA promoter demonstrate repression by HMG-I (Y), and suggest a model of Il-4-inducible derepression. Based on these results, a first goal of this proposal is to characterize the mechanisms by which HMG- I (Y), a subunit of NF-BRE, interferes with TBP function and controls the germline epsilon promoter. This investigation will be performed in vitro by studying protein: protein interactions, and using in vitro transcription reactions. We have discovered that Il-4 signaling is coupled to HMG-1 (Y) phosphorylation by a step sensitive to the immunosuppressive rapamycin. Thus, a second goal is to investigate the functional effects of increased HMG-I(Y) serine phosphorylation signaled by IL-4. A third goal is to identify the HMG-i (Y)-associated subunit of NF-BRE to complete our understanding of its structure and the basis for its developmental regulation in the B lineage. An analysis of the regulation of HMG-1 (Y), identification of the other subunit protein(s) with which it interacts, and a characterization of the interplay among HMG-1(Y), NF-BRE, and other transcription factors will enhance our ability to control IL-4 related signal transducers and NF-BRE will enable us to manipulate immune function in animal models. These later studies will employ transgenes targeted to specific cell types, or chemical inhibitors.